Pregnant women who drink two cups or more of coffee a day are at an increased risk of miscarriage, suggests a new U.S. study.

Researchers found women who drank 200 mg or more of caffeine — whether from coffee, tea, caffeinated pop or hot chocolate — had twice the risk of miscarrying compared to the study subjects who consumed no caffeine.

U.S. researchers say pregnant women double their risk of miscarriage when they drink 200 mg of caffeine a day, equivalent to two cups or more of coffee.
(CBC)

Two or more cups of regular coffee or five 355 ml cans of caffeinated soda are equivalent to 200 mg or more of caffeine.

While other studies have suggested a link between caffeine and miscarriage, the researchers say theirs is the first to control for other potential risk factors — including age, race, education, household income, marital status, smoking and alcohol consumption.

The study out of the Kaiser Permanente Division of Research is published in the online issue of American Journal of Obstetrics and Gynecology, a peer-reviewed publication. Kaiser Permanente is the largest health plan in the United States.

The study, which ran from October 1996 through October 1998, tracked 1,063 pregnant women in San Francisco, examined caffeine's effect on the women who never changed their pattern of caffeine consumption during their pregnancy. The study followed the women only up to 20 weeks of pregnancy.

The increased risk of miscarriage appeared to be due to the caffeine itself, rather than other chemicals in coffee, because caffeine intake from non-coffee sources such as caffeinated pop, tea and hot chocolate showed a similar increased risk of miscarriage.

"The main message for pregnant women from these findings is that they probably should consider stopping caffeine consumption during pregnancy because this research provides clearer and stronger evidence that high doses of caffeine intake during pregnancy can increase the risk of miscarriage," said De-Kun Li, the study's lead investigator.

Caffeine crosses through the placenta to the fetus, but can be difficult for the fetus to metabolize because of the undeveloped metabolic system.

Dr. Gideon Koren, director of the Motherisk Program at Toronto's Hospital for Sick Children, cautioned that women shouldn't over-react to the study.

"These studies don't prove causation. They prove association. It's not the same," he told CBC News. "I don't think women should stop drinking coffee. Pregnancy is not the name of a disease the last time I heard … just don't overly indulge."